Stanford, CA (Sports Network) - Serena Williams, the reigning Wimbledon, Australian Open and U.S. Open champion, was upset in three sets by Australian Samantha Stosur in the quarterfinals Friday at the $700,000 Bank of the West Classic.
Stosur, who has yet to win a career title on the WTA Tour, earned a 6-2, 3-6, 6-2 win over the top-seeded Williams on the hardcourts at Taube Family Tennis Stadium.
Williams' sister, second-seeded Venus, who titled here in 2000 and 2002 and was the runner-up in 1998, 1999, 2004 and 2005, moved into the semifinals by beating Russian Maria Sharapova, 6-2, 6-2.
The last time Serena played singles against Stosur, she saved four match points before overcoming the Aussie in the first-round of a tournament in Sydney earlier this year.
"It was really satisfying. I was just pleased with the way I played," said Stosur. "Even if I didn't win today, I would have walked off the court knowing I played a good match and she needed to come up with something really special to beat me. So overall I'm just really happy."
For Serena, it was her first loss since falling to Russian Svetlana Kuznetsova in the quarterfinals at the French Open.
"She had a lot of lucky shots today," said Serena. "That's kind of her game; she's a big framer. That's obviously all talent. But she's mastered that."
Third-seeded Russian Elena Dementieva eased into the final four by besting Slovakian Daniela Hantuchova 6-2, 6-4. Dementieva will next face Venus.
In the other quarterfinal encounter, fourth-seeded Serbian Jelena Jankovic was upset by eighth seed Marion Bartoli of France, 3-6, 7-6 (7-3), 6-3.
This week's Stanford champion will pocket $107,000.